1. Field of the Invention
This invention relates to the field of data entry devices for use in hostile environments.
2. Prior Art
Data entry devices such as keyboards must often be used in industrial settings where the environment may be hostile, such as in chemical plants, on offshore and land oil drilling rigs and in factories. In such settings, the device may be subjected to a variety of human and environmental abuses including volatile or corrosive gases, hazardous chemicals and high pressure water spray. A data entry device used in such an environment should therefore be durable and internally purgeable and should have its electronic components electrically isolated from the external atmosphere.
Prior art devices have included that disclosed in U.S. Pat. No. 3,448,419 issued to Myatt. In Myatt, reed switches are protected from adverse weather conditions by mounting them beneath a magnetically permeable plate. The reed switches are operated by permanent magnets attached to the end of spring-loaded keys whose shafts protrude through a mounting plate placed above the mgnetically permeable plate. Flexible bellows-like covers extend from the button of each key to the mounting plate in order to protect the springs, the shafts and the components beneath the mounting plate from exposure to weather conditions. However, if the flexible bellows-like cover surrounding the shaft and spring of any key becomes damaged, the mechanical and magnetic components not located beneath the magnetically permeable plate would be exposed to environmental conditions because of the presence of the hole in the mounting plate through which the shaft of the key must move. Further, it is believed that bellows-like covers are not only highly susceptible to accidental damage but prone to failure merely from repeated flexing. It is therefore not believed that the arrangement disclosed in Myatt is particularly suitable for use in a hostile industrial environment where not only resistance to weather conditions but durability despite physical and chemical abuse is necessary.
In U.S. Pat. No. 4,203,013 issued to Serras-Paulet, the use of magnetic Hall-effect semi-conductors as switches is suggested. Each of the suggested embodiments in Serras-Paulet uses keys having shafts which pass through apertures in a plate. In Serras-Paulet, a layer of magnetic rubber placed on the underside of the apertured plate is used to return the keys of the keyboard to their unpressed condition through the attraction of a magnet placed on the lower part of the key to the magnetic rubber layer. In the embodiment shown in FIG. 5 of that patent, a thin additional rubber sheet having a thicker portion located on top of the shaft of the key is used for fluid-tight sealing. This rubber layer is a layer separate from the magnetic rubber layer described previously and is used only to provide fluid-tight sealing. However, even in this embodiment, Serras-Paulet uses separate keys which pass through apertures in a plate.
In U.S. Pat. No. 3,750,062 issued to Goto, reed switches are mounted below the positions of a switch board and are operated by bringing a small magnet attached to the finger of the operator into contact with the switch board at the appropriate locations. The surface of the switch board, according to the patent, may be made of a substance such as rubber, plastic or cloth into which the magnet, attached to a finger of the operator, may be pressed in order that switching occur. Requiring that an operator key in data by the use of a magnet on the tip of the operator's finger is not appropriate in industrial type environments where the magnet may be lost or misplaced, or the operator may be wearing gloves.
Compared with the prior art devices discussed above, the present invention provides a data entry device of much simpler construction and of higher reliability when used in hostile environments. In the present invention, keys having springs and shaft susceptible to corrosive gases and liquids are eliminated, while the electronic components are mounted behind a magnetically permeable stainless steel plate which provides part of a fluid-tight enclosure around all the electronics. Even the magnets mounted beneath the keys of the present invention may be completely protected from the hostile conditions of an industrial environment by encasing them completely within the elastomer keyboard matrix.